The present invention relates to a leading edge structure for aircraft wings and empennages.
Wings and empennages (vertical and horizontal) are primary structures sized in a way such as to have a rigidity and robustness suitable for the aerodynamic loads to which it can be subjected during flight, landing and takeoff. The leading edge structure of a wing and of an empennage must also be sized so as to withstand the impact with a flying object.
The so called “bird strike” test is regulated by FAR 25.631 which states that: if an aircraft suffers an impact with a bird, having a defined weight and at a predetermined speed, after such condition there must be no damage on the primary structures that could prevent the aircraft from safely landing at the nearest available airport. Since whilst flying in cruise conditions the first structural element which can potentially undergo such types of impact is the leading edge, this structure must fully comply with the aforementioned standard. In addition to the aforementioned requirement, it is necessary for the leading edge to be suitably sized so as to withstand aerodynamic loads applied to it.
The aforementioned structures are commonly designed and manufactured in a manner such as to prevent the leading edge from being pierced, and thus to avoid possible damage to the structure behind it, or, in the case in which piercing is foreseen, they are designed so that the damage is locally limited.
Conventionally, wing structures are made from aluminium (shell thicknesses generally of only a few millimeters) reinforced by transverse elements which have the main task of giving the profile its shape. In these types of structures the task of absorbing energy is carried out, apart from by the—generally curved—shape of the leading edge, it is especially carried out by its thickness. The greater the thickness, the higher the amount of energy absorbed.
Other wing structures use hybrid material such as Glare® (fibreglass and aluminium laminate) also for the leading edge. In these other structures, the energy is absorbed as well as by the curved shape of the leading edge, particularly by the coupling between fibre-glass and aluminium. Fibre-glass contributes in an important way to absorbing a substantial fraction of the elasto-plastic deformation energy due to impact; this effect is called “bridging” in the field of the materials applied to aircrafts.